1. Field of the Invention
The present invention relates to a wireless communication apparatus which transmits a transmission symbol spread and multiplied by a code sequence.
2. Description of the Related Art
A recent wireless communication system performs wireless communication by letting a plurality of base stations use the same frequency band. In such a wireless communication system, interference from an adjacent base station or interference to an adjacent base station (inter-cell interference) sometimes affects the wireless communication performance. As one means for reducing the influence of this inter-cell interference, there is available a symbol spreading means for transmitting a data symbol to be transmitted by using a plurality of transmission symbols obtained by copying the data symbol. Using this means can improve the wireless communication performance in accordance with the number of copies. In order to improve the wireless communication performance by using the spreading means, it is necessary to cause a plurality of wireless communication apparatuses, e.g., wireless communication terminals which perform wireless communication with adjacent base stations or the same base station to multiply copied data symbols by predetermined code sequence called a scramble code sequence or the like. In addition, it is necessary to use different sequences as the scramble sequences for the respective wireless communication apparatuses.
In general, a sequence having randomness such as a pseudo-random sequence is used as the above scramble sequence, and hence the above inter-cell interference is randomized. This makes it possible to improve the wireless communication performance by spreading.
In a multicarrier wireless communication system typified by an orthogonal frequency division multiplexing (OFDM) system, which performs wireless communication by mapping transmission data on a plurality of frequency subcarriers, it is necessary to perform the above symbol spreading within the range of a plurality of frequency subcarriers and a plurality of symbols. As a scramble sequence multiplication method in this case, there is available a method of making the scramble sequence length equal to or more than the total number of frequency subcarriers and multiplying each element of the sequence for each frequency subcarrier (see, for example, [JP-A 2002-204217 (KOKAI) (Japanese Patent No. 3553038), FIGS. 3 to 5]).
In the above conventional technique, however, a plurality of symbols obtained by symbol spreading are sometimes multiplied by the same element of a scramble sequence. This reduces the effect of randomization of inter-cell interference which is obtained by making different wireless communication apparatuses multiply different scramble sequences. As a result, this also reduces the effect of improving the wireless communication performance by spreading the data symbol to be transmitted.